Ship propulsion system comprising a control that is adapted with regard to dynamics

ABSTRACT

A ship propulsion system includes a ship electrical system and an electric propulsion system that is supplied with power from the electrical system, and which is equipped with a cascade control for the propeller motor. The rotational speed of the propeller motor is preset by a higher-order controller whose command variable is issued by the throttle lever. Filters means are provided for suppressing impairments to the ship&#39;s operation that result due to the high dynamics of the propulsion system.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/DE01/00027 which has an Internationalfiling date of Jan. 8, 2001, which designated the United States ofAmerica and which claims priority on patent Application Ser. No. 100 01358.9 filed Jan. 14, 2000, Ser. No. 100 11 602.7 filed Mar. 10, 2000,Ser. No. 100 11 601.9 filed Mar. 10, 2000, Ser. No. 100 11 609.4 filedMar. 10, 2000, and Ser. No. 100 63 086.3 filed Dec. 18, 2000, the entirecontents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present application generally relates to ship propulsion systems.

BACKGROUND OF THE INVENTION

Propulsion devices for ship propellers with an electric propeller motoruse rotation speed regulators for closed-loop control. A rotation speednominal value is preset using the control lever on the bridge. Upstreamof the input to the regulator, the rotation speed nominal value(reference variable) is compared with the rotation speed value at thattime in order to determine from this a control error, which is suppliedto the regulator. The output signal from the regulator is passed as acontrolled variable to an actuating device, via which the propellermotor is connected to the current source.

When synchronous machines are used for propulsion, the actuating deviceis in the form of a frequency changer/converter, which uses thegenerator voltage from the diesel generator system to produce a suitablepolyphase, variable frequency supply voltage. The converter circuit isdesigned such that the interconnection of the converter and synchronousmachine results in a similar response to that from a DC machine whosecurrent is controlled via a DC controller. The signal which is passed tothe control input of the DC controller governs the current drawn by theDC machine. In the same way, the control signal from the regulatorgoverns the current used to operate the synchronous machine.Asynchronous machines can also be supplied with electrical power, andcan be used for ship propulsion, in the same way. It has now been foundthat propulsion systems of this type are relatively stiff, that is tosay they are also able to regulate out minor rotation speed fluctuationswhich are within one propeller revolution.

The reason for rotation speed fluctuations and/or angular velocitychanges is the behavior of the ship's propeller in the water which isflowing past the hull while the ship is in motion and whose speedprofile is not three-dimensionally uniform. During their rotationalmovement, the propeller blades in some places move through the skeg orpropeller-shaft stay on the ship's hull while, in the rest of theirrotational movement, different water flow speeds impinge on them.

From the hydrodynamic point of view, the change in the load on theship's propeller with time can be described by its wake field. Thefluctuation in this load which is caused by the skeg or propeller-shaftstay on the ship's hull is once again evident in the inhomogeneity ofthe wake field of the propeller, which in turn results in a fluctuatingangle of advance during revolution of the propeller blade.

Thus, the torque fluctuates cyclically, resulting in the ship'spropeller having a fluctuating angular velocity which is regulated outby the rotation speed regulator, or by the current regulator that issubordinate to it, in order to keep the rotation speed of the ship'sscrew as exactly constant as possible at the preselected nominalrotation speed value. The frequency of the torque fluctuationscorresponds to the shaft rotation speed multiplied by the number ofblades on the propeller. The torque fluctuation is transmitted from thepropulsion motor to its anchorage, and thus to the ship's hull. A torquereaction also occurs on the diesel generator system. In consequence,parts of the ship structure are caused to oscillate at the fundamentalfrequency of this pulsating torque and, as a result of the mechanicalcharacteristics, the resonance of the ship's hull is not negligible atthe relevant frequency. The vibration that this results in is not onlyannoying to those on the ship, but also results in a considerable loadon the entire structure of the ship and its cargo, and should thus beavoided

In the past, attempts have been made to calculate the weak points forsuch oscillations using the so-called finite element method and toreinforce the critical areas determined in this way by the use of tonsof steel. This method is on the one hand expensive and on the other handreduces the maximum permissible cargo weight and the useful cargo areaof the ship, while increasing the fuel consumption and, furthermore,although it can reduce those effects of the oscillations produced by thepropulsion that destroy material, it does not eliminate the cause,however.

Closed-loop rotation speed control, which keeps the rotation speed ofthe ship's propeller at the preselected nominal rotation speed value asexactly as possible, leads to a further negative effect.

Since the inhomogeneity of the wake field fully reflects the fluctuationin the angle of advance of the propeller, the cavitation safety marginof the propeller is reduced, since the operating point of a propellerbecomes closer to its cavitation limit, or may even exceed it.Particularly in the region of a skeg or propeller-shaft stay on theship's hull, the operating point of the propeller may reach or exceedthe cavitation limit and thus initiate cavitation, which can then leadto considerable damage to the ship and, in particular, to the propeller.Cavitation also leads to unacceptable pressure fluctuations and noise,which considerably reduce, in particular, the useful value and comfortof passenger, research and naval ships.

The rotation speed of ship's propellers which are driven via electricmotors can be adjusted very quickly. Rapid adjustment of the rotationspeed also leads, inter alia, to cavitation on the propeller blades. Inthis case, the rate at which the rotation speed is adjusted depends onthe speed of motion of the ship, that is to say on the incidence speedat which the water strikes the propeller.

For this reason, the ramp-up transmitters are provided, which, from thecontrol engineering point of view, are located between the control leverand the nominal value input to the regulator.

When the actual rotation speeds of the ship's propeller increase, itsdynamic response changes considerably. Since the family of curves forthe propeller (transition from the towing curve to the free drive curve)follow a square law, the maximum permissible dynamic response of theship's propeller decreases more than proportionally as the actualrotation speeds rise.

In the case of ship's propeller propulsion devices which are known fromthe prior art, the ramp-up time which is governed by the ramp-uptransmitter is increased in one to three stages as the rotation speed ofthe propulsion motor for the propeller increases, in order to keep theexcess rotation speed within the maximum permissible range of thepropeller curve.

Furthermore, with regard to the power requirement, the electricalpropulsion system also has to take account of the generator excitation.Its time response is slower than the possible dynamic response of theelectrical machine for the ship's propeller.

Taking account of these two boundary conditions, the ramp-up transmitterfrom the prior art is designed as follows:

Starting from a rotation speed of zero, the propeller motor first of allaccelerates without any restriction, that is to say optimally. The powerconsumed by the propeller rises more quickly while ramping up with aconstant ramp-up time, and finally reaches a current limit in therotation speed regulator, in order to avoid overloading the dieselgenerator system. At the end of the first stage of the ramp-uptransmitter, a change is made to a different ramp-up time. Theacceleration power which is available from the electrical propulsiondecreases to virtually zero. This results in a sudden change in thepower consumption from the diesel generator system, which it must, butcannot necessarily, regulate out. This leads to frequency and/or voltagefluctuations in the on-board power supply network.

At least in the first phase of the ramp-up time, the propulsion devicedraws electrical power from the diesel generator system, which in somecircumstances leads to failure of the supply to the rest of the on-boardpower supply network.

When changing from the first ramp-up phase to the second ramp-up phasefor acceleration of the ship, this results in the disadvantage that theship is accelerated to only a very minor extent in certain rotationspeed ranges.

With the propulsion device as described above, the current limit for theelectrical machine for the propeller occurs at approximately 30% of therated torque over the respective ship's propeller curve. The regionbetween the current upper limit of the electrical propulsion machine andthe calculated ship's propeller curve is required in order to provide amargin for heavy seas and/or ship maneuvers in addition to theacceleration torques which are required for the procedures involved inaccelerating the ship.

The ramp-up transmitters which until now have been controlled in stagesfor propulsion devices for ship propellers are unable to allow theelectrical machine which is driving the propeller to produce a definedacceleration torque during acceleration processes. In fact, over widerotation speed ranges, they allow only the respective current limit atthat time. The reason for this is that the acceleration time for theship is several times the ramp-up time of the ramp-up transmitter type.

As has already been mentioned above, the diesel generator system has apower response with respect to time which can vary only more slowly thanthe power consumption of the electrical machine for the ship'spropeller. Thus, in addition to the restrictions resulting from thepropeller curve, it is also necessary to take account of therestrictions which result from the maximum dynamic response of thegenerator system.

When designing diesel engines for diesel generator systems for ships,the requirements of the International Association of ClassificationSocieties (IACS) are taken into account with regard to the loadresponse. The three-stage load change diagram associated with theserequirements has a considerable influence on the dynamic response of thepropulsion device for the ship's propeller in the case of present-daydiesel engines, which use high boost levels. A further exacerbatingfactor is that the values that are known there are often no longerachievable nowadays, particularly in the upper power range, owing toinadequate maintenance and owing to the use of relatively poor qualitybunker oil. The maximum possible dynamic response for power emission onthe shaft of the diesel engine therefore, based on experience, decreaseswhen the ship has been at sea for a lengthy time.

A further time gradient in the power emission from diesel engines, whichis not specified according to the IACS or in any other generally bindingform, is the thermal load capacity of the diesel engine. A smooth loadchange on a diesel engine at its operating temperature, from zero to therated power or from the rated power to zero, may be carried out onlywithin a minimum time, which is dependent on the physical size of therespective diesel engine. These times have fluctuated severely as afunction of the physical size.

The time profile must not be exceeded, even in places, since, otherwise,this can lead to damage to the diesel engine.

The minimum times mentioned above may be between 10 and 20 seconds forsmall diesel engines, and up to 120 seconds for large diesel engines.

The converters/frequency changers which are connected between the dieselgenerator system and the electrical machine for the ship's propellerrequire a control wattless component. The control wattless component isdependent on the load. Examples of converters/frequency changers such asthese include current intermediate circuit converters, directconverters, converters for DC machines and the like.

The wattless component is supplied from the synchronous generators inthe diesel generator system. The time gradient of the load-dependentwattless component for the converters mentioned above with a controlwattless component may vary 15 to 25 times more quickly than theterminal voltage of the synchronous generators, and the generator systemcannot follow this. In particular, time is required to educe theexcitation field for the synchronous generators.

If the dynamic limits of the diesel engines are exceeded when drivingship propellers, their rotation speed fluctuates, and hence thefrequency of the on-board power supply network that is fed from thediesel generator system, to an unacceptable extent. It is alsoimpossible to preclude damage to the diesel engines when the closed-looprotation speed control for the generator system is intended to, or must,keep the frequency of the on-board power supply network within apermissible range, while ignoring the dynamic limits. If the dynamiclimits of the synchronous generators are exceeded, the voltage of theon-board power supply network also fluctuates so severely that itdeparts from the permissible tolerance band.

According to the prior art, experiments have already been carried outbased on multistage or continuous changes to the ramp-up times of therotation speed nominal value and/or the current nominal value in thecourse of trial runs for such a long time that it has been possible toregard the interaction between the electrical machine for the ship'spropeller and the diesel generator system as being satisfactory, withoutany unacceptable frequency or voltage fluctuations occurring in theon-board power supply network. In this case, it was often possible onlyto achieve optimization at certain operating points. There was no fixedrelationship between the adjustment capabilities in the closed-loopcontrol for the electrical machine for the ship's propeller and itsdynamic effect on the diesel generator system in the on-board powersupply network. The time profile for the reduction in the load on thediesel generator system was rarely taken into account, and was rarelyadjustable, in the closed-loop control for the propulsion device for theship's propeller.

SUMMARY OF THE INVENTION

Against this background, an object of an embodiment of the invention isto provide a ship propulsion system for a ship which has an electricalon-board power supply network. Preferably, one is provided which doesnot lead to reductions in comfort and/or to adverse effects on shipoperation.

In particular, one aim is to make it possible to match, and to match thedynamic response of the ship propulsion system to the various types ofboundary conditions mentioned above in a better manner.

According to an embodiment of the invention, an object may be achievedby developing a ship propulsion system. The reductions in comfort may beexpressed in the form of oscillations in the ship's structure and/or inflickering lighting. The device according to an embodiment of theinvention ensures that no fluctuations occur in the instantaneous valueof the on-board power supply network voltage and/or in its frequency,going beyond a reasonable extent, irrespective of the speed at which thecontrol lever and/or the rudder angle is adjusted.

Fluctuations could thus occur in the on-board power supply networkvoltage if the control lever were reset to zero too quickly, with theload being removed from the generator system more quickly than ispossible to reduce the excitation of the synchronous machine.Conversely, fluctuations can also occur if the control lever is movedtoo quickly in the direction of high motor power. As a rule, thefrequency falls in this case, because the diesel engine cannotaccelerate sufficiently quickly.

Rudder movements have a similar effect on the generator system and/orthe on-board power supply network. As the rudder is deflected, the loadon the propeller rises, while the load on the propeller decreases whenthe rudder is moved to the null position.

Excessively rapid acceleration processes on the propeller can also leadto considerable noise, if the acceleration leads to cavitation on theship's propeller.

The coupling of noise from the ship's hull and from the propeller intothe water represents environmental pollution which propagates over wideareas and can considerably restrict the use of ships in correspondingprotected areas, for example in the Arctic and Antarctic. The reductionin the noise emission as described above makes it possible, inparticular, for passenger ships to be operated in traveling regionswhich are financially of particular interest and in which the faunaliving there remain protected against dangerous noise and pressurefluctuations, by virtue of an embodiment of this invention.

In order to counteract vibration which is produced because the ship'spropeller is subject to torque fluctuations in the moving water, thefilters may include first filters which are set up to suppress amplitudefluctuations in the signal at the control input on the actuating device.Torque fluctuations result in changes to the angular velocity of thepropeller shaft, which leads to corresponding ripple on the signalsupplied from the rotation speed transmitter. Without an embodiment ofthe invention, the ripple would be reflected directly in the controldifference and would lead to the current for the propeller motor, andhence its drive torque, fluctuating in accordance with this controldifference.

The first filters filter out this ripple, that is to say the propulsionsystem may be provided with the capability to allow the rotation speedto flex when the propeller blades run into a high flow resistance, andallow the rotation speed to be resumed once the “difficulty impedingmovement” has disappeared.

The filters which can be used for this purpose may be amplitude filterswhich pass on a signal change only when the signal change has exceeded acertain level. A filter such as this may be, for example, in the form ofa diode characteristic. The other option is to use a frequency filterwhich acts as a low-pass filter and filters out the ripple that issuperimposed on the control difference.

The frequency filter may be designed to be adaptive in such a way thatthe cut-off frequency varies with the rotation speed of the propellershaft, or the voltage threshold varies with the basic value orequivalent value of the input variable. This ensures that an adequatedynamic response is provided in all rotation speed ranges, without thesuppression of the ripple having any influence on the closed-loopcontrol dynamic response, or the ripple penetrating through to theactuating device in another rotation speed range.

The first filter may be arranged between the regulator input and therotation speed sensor, in the signal path of the signal with the controldifference, or at the output of the regulator between the regulator andthe control input of the actuating device. It is also possible for thefilter to be implemented in the actuating device.

If the filters are in the form of an amplitude filter, they areexpediently located in the signal path for the control difference. Theclosed-loop control device preferably has a PI control response.

The closed-loop control device may be designed in a classic manner as ananalog closed-loop control device, or such that it operates digitally.

In the case of a PI regulator, the desired filter characteristic isachieved by feeding back the output signal from the closed-loop controldevice in antiphase to the input. The actuating device for the propellermotor may itself once again be in the form of a regulator. The controlsignal for the actuating device in this case preferably has thesignificance of a current nominal value. That is to say, the currentcontrolled may be that emitted from the actuating device to thepropeller motor, hence controlling the torque which is emitted by thepropeller motor. Such open-loop control is also possible when thepropeller motor is in the form of a synchronous machine and theactuating device is in the form of a frequency changer or converter.Circuits that are suitable for this purpose are known from the priorart.

If feedback is used in order to filter the ripple, this feedback isexpediently set such that it results in a steady-state control error ofapproximately 0.2 to approximately 3% at the rated load. If this controlerror has a disturbing effect, it can be compensated for by means of anappropriately corrected nominal value. The nominal value compensationmay be carried out as a function of the estimated load.

In order to suppress cavitation phenomena on the ship's propeller as aresult of excessively fast acceleration, the filters expediently havesecond filters, which are in the form of controlled ramp-uptransmitters. The ramp-up transmitter is used to match the rate ofchange of the rotation speed of the propeller shaft to the maximumpermissible level.

For this purpose, the second filters may contain a characteristic inorder that the rate of rise of the nominal value signal arriving fromthe control lever can be slowed down as a function of the rotation speedof the propeller motor. For this purpose, the second filters may bearranged between the input of the closed-loop control device and thecontrol lever. At this point, it has no adverse effect on the controlresponse, comprising a closed-loop control device, the actuating deviceand the ship's propeller.

The characteristic of the second filter may be considered continuous inthe sense that it has no discontinuities. It does not necessarily needto be smooth in the mathematical sense, but may also be approximated inthe form of a string of polygons. The only essential feature is that thetransitions within the string of polygons have no discontinuities. Thecharacteristic may be a square-law characteristic with an offset.

In order that the ship can still be maneuvered well in the low speedrange, the characteristic may be designed, at least in the lowerrotation speed range, such that the ramp-up time is constant and short,and rises only slightly with the rotation speed of the propeller. Thepropulsion system is then effectively “attached” directly to the controllever.

In a higher rotation speed range which starts at approximately 25 to 45%of the rated rotation speed, the ramp-up time increases with, or fasterthan, the rotation speed of the propeller motor. In consequence, thepossible angular acceleration decreases the higher the rotation speed ofthe ship's propeller, irrespective of the rate at which the controllever is moved.

In an upper rotation speed range which starts, by way of example, athalf the rated rotation speed, the rate at which the rotation speed ofthe propeller motor can increase is restricted even further, that is tosay the ramp-up time increases even faster with the rotation speed, thanin the rotation speed range below this.

However, it would also be feasible to control the rotation speed of thepropeller motor such that it rises firstly in accordance with a squarelaw with a short ramp-up time and then with an increase in rotationspeed of the propeller motor, in order that the rate at which therotation speed of the propeller can increase is slowed down inaccordance with a square-root function plus an offset.

The second filter may be in digital form using a microprocessor, or maybe designed such that it operates in analog form.

As already mentioned in the introduction, reductions in comfort alsooccur when the on-board power supply network voltage fluctuates tooseverely, because the generator system cannot follow the change in thepower requirement for the ship propulsion sufficiently quickly.Excitation of synchronous machines and, in particular, reduction in theexcitation of synchronous machines, require time. If the powerconsumption by the ship propulsion changes more quickly than it ispossible for the excitation/reduction in excitation to take place, theon-board voltage departs from the permissible tolerance band, and thisunnecessarily loads, or overloads, the appliances which are connected tothe on-board power supply network. The diesel drive for the generatorscannot follow this sufficiently quickly either, and this can lead todamage to the diesel engine.

In order to eliminate adverse effects resulting from this, the filtersmay have third filters, which restrict the rate of change of the powerconsumption by the propeller motor, to be precise to values which theon-board power supply network system can follow without any problems.

The third filter may once again be arranged either in the signal path ofthe nominal value signal, that is to say between the regulator and thecontrol lever, downstream of the closed-loop control device or in theactuating device itself. The arrangement downstream from the regulatoror downstream from the subtraction point has the advantage of alsoslowing down state changes which are caused by changes in the propellerload. Such changes in the propeller load occur when moving the rudder orwhen switching off or throttling down a propeller in multishaft systems.

The third filters have expediently been embodied in digital form, basedon microprocessors. The third filters may also be of classic design, andmay operate in analog form.

The third filters may be designed such that they limit the rate ofchange, when the control lever is moved in the direction of greaterpower consumption, to values which are different to those used when thecontrol lever is moved in the direction of low power values.

The limit to the rate of change decreases at least in an upper powerrange or rotation speed range of the propeller motor.

The rate of change which the third filters allow may also be dependenton the number of generators feeding the on-board power supply network. Afurther influencing variable may be the operating state of the system,that is to say whether the system is already in a warmed-up steady stateor is still in the warming-up phase, that is to say it is dependent onthe total operating time. Finally, a further influencing variable is theload on the generator system, that is to say whether the load is in thelower, the medium or the upper power range of the diesel engines.

In order that the ship remains maneuverable and, in addition, that nocontrol oscillations occur which are caused by the limiting of the rateof change, the third filters may be designed such that they provide awindow within which the third filters do not influence the rate ofchange at which the signal of the control input of the actuating devicechanges. A window such as this is particularly expedient when the thirdfilters are located in the signal path between the closed-loop controldevice and the actuating device. If the third filters are locatedbetween the control lever and the nominal value input of the closed-loopcontrol device, such a window is in some circumstances unnecessary.Those combinations of features which are not reflected by an exemplaryembodiment are also intended to be covered by the scope of protection.

Where the patent claims refer to a “ship's propeller” and a “propellermotor”, then it is obvious to those skilled in the art that theinvention is not restricted to a single motor and a single ship'spropeller, but that a number of motors or ship's propellers may also becontrolled jointly or separately from one another. Furthermore, theinvention relates equally to surface vessels and underwater vessels.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are illustrated in the drawings,in which:

FIG. 1 shows a block diagram of a ship propulsion system with firstfilters for reducing oscillations in the hull caused by the behavior ofthe propeller in the water,

FIG. 2 shows the closed-loop control device as shown in FIG. 1, in theform of a detailed block diagram,

FIG. 3 shows the transmission response of an amplitude filter,

FIG. 4 shows a block diagram of a ship propulsion system with secondfilters for matching the dynamic response to the dynamic response of theship's propeller,

FIG. 5 shows the transmission characteristic of the second filters,

FIG. 6 shows the profile of the ship's acceleration for a ship which isequipped with the propulsion system according to an embodiment of theinvention,

FIG. 7 shows a block diagram of a ship's propulsion system which isprovided with third filters, in order to match the dynamic response ofthe propeller motor to the dynamic response of the generator system,

FIG. 8 shows characteristics of the third filters,

FIG. 9 shows the profile of the ramp-up time and ramp-down time of thecurrent nominal value, for different numbers of feeding generators,

FIG. 10 shows the profile of the window for the third filters in whichthe rate of change is not restricted, related to a continuous value, and

FIG. 11 shows the profile of the window as a function of the number ofactive generators.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a block diagram of an electrical ship propulsion system.The block diagram shows only those parts which are significant to theidea of embodiments of the invention. The detailed circuit diagram ofthe ship propulsion system is, of course, considerably more complicated,but this would detract from the illustration of all the details of onlythe idea of embodiments of the invention, and would make understandingmore difficult.

The ship propulsion system includes a control lever 1, which is arrangedon the bridge, a closed-loop control device 2, a propeller motor 3 fordriving a ship's propeller 4, a schematically indicated on-board powersupply network 5 and an actuating device 6, via which the propellermotor 3 is connected to the on-board power supply network 5. In thepresent documents, the term control lever is used to represent alldevices by means of which the speed of motion is preset at a highcontrol level, such as automatic systems, that is to say a “cruisecontrol” for ships.

The control lever 1 supplies an electrical signal, which corresponds tothe rotation speed of the ship's propeller 4, as a reference variablevia a connecting line 7 to a nominal value input 8 of the closed-loopcontrol device 2. The closed-loop control device 2 contains an additionnode 9 as well as a PI regulator 10, whose output 11 is connected to aninput 12 of the actuating device 6.

The closed-loop control device 6 receives the actual value signal via aline 13, which is connected to a rotation speed sensor 14. The rotationspeed sensor 14 is composed of a digitally operated rotation speedtransmitter 15 and a digital/analog converter 16 with rotation directionidentification.

The rotation speed transmitter 15 is connected to a propeller shaft 17,on which the propeller motor 3 works and on which the ship's propeller 4is seated such that they rotate together. The digital/analog converter16 uses two phase-shifted cyclic digital signals coming from therotation speed transmitter 15 to produce, in a known manner, a signalwhich is proportional to the rotation speed and with a mathematicalsign, and this is passed to the line 13. This signal, which isproportional to the rotation speed of the ship's propeller 4, iscompared at the addition node 9 of the closed-loop control device 2 withthe signal coming from the control lever 1.

The rotation speed sensor 14 may, alternatively, be an indirectmeasurement system. The rotation speed is detected by means of the timeprofile of the current and voltage, preferably in the actuating device 6or in the connecting line 19 for the propeller motor. The differencewhich is obtained from this is processed in the PI regulator 10, inaccordance with its characteristic. The control response of a PIregulator is known, and does not need to be explained in any more detailat this point.

The actuating device 6 is once again itself designed in the form of aregulator, and contains a controller 18, for example composed of GTOsconnected in a bridge circuit, which are connected in series between thepolyphase, for example three-phase, on-board power supply network 5 andthe propeller motor 3.

The propeller motor 3 is, by way of example, a synchronous machine, andthe controller 18 is controlled such that it receives an appropriatepolyphase, variable frequency AC voltage. A current sensor 21 is locatedin a connecting line 19 between the controller 18 and the propellermotor 3, and is connected via a line 22 to a converter circuit 23. Thecurrent sensor 21 may likewise be arranged on the input side of thecontroller 18.

The converter circuit 23 produces a DC signal from the AC signal whichis detected by the current sensor 21, and this DC signal corresponds, byway of example, to the total root mean square value of the currentflowing into the propeller motor 3. The converter circuit 23 accordinglyemits at its output 24 a DC signal which is supplied via a line 25 to anaddition node 26. In the addition node 26, the signal from the currentsensor 21, which is proportional to the current, is compared with theoutput signal from the closed-loop control device 2, for which reasonthe other input of the addition point 26 is connected to the input 12 ofthe actuating device. The difference obtained in this way between thecurrent nominal value and the current actual value is passed via a line27 to a further PI regulator 28, whose output signal is fed via a line29 into a drive circuit 31, which uses the regulator output signal toproduce control signals, in the correct phase, for the controller 18,which is connected to the drive circuit via a multipole line 32.Theactuating device 6 in the present case forms a converter. The propellermotor may also be an asynchronous machine, instead of the synchronousmachine. It is likewise possible to use a DC machine, which may befedwith alternating current.

The flow field of the water flowing past the ship's propeller 4 differsin three dimensions. The nonuniform flow distribution prevents theship's propeller 4 from always experiencing the same resistance torquesin the water throughout one complete revolution. When its propellerblades enter certain flow areas, they meet an increased resistance. Thisthree-dimensionally different resistance leads to torque fluctuations ifthe propulsion shaft 17 is driven at an exactly constant rotation speed.

The constant shaft rotation speed results in opposing torques beingcreated in the propeller motor 3, and these are transmitted to the shipstructure. As soon as the propeller blade emerges from the area of highflow resistance once again, the torque falls until the next propellerblade enters this flow area. The torque which the propeller motor 3 mustapply thus fluctuates cyclically at a frequency which is equivalent tothe product of the shaft rotation speed and the number of propellerblades.

The torque fluctuations result in fluctuations in the angular velocity,and are detected as angular velocity changes by the rotation speedsensor 14. The closed-loop control device 2 tries to regulate out therotation speed fluctuations, in order to drive the propeller shaft 17 ata constant rotation speed. This results in considerable vibration in theship's hull.

The signal which is passed to the control input 12 of the actuatingdevice 6 is composed, assuming that no further measures are taken, of aDC component on which a ripple is superimposed, corresponding to thetorque fluctuations. According to an embodiment of the invention, theclosed-loop control device is equipped with first filter(s), whosepurpose is to suppress the previously mentioned ripple.

As soon as the signal reaching the control input 12 is free of thisripple, the propeller motor 3 can drive the ship's propeller 4 with aconstant torque. The angular velocity of the propeller shaft 17 will nowvary cyclically corresponding to the “instantaneous resistance tomovement” of the ship's propeller 4 in the water. For this purpose, thepropeller motor 3 is largely free of cyclic torque fluctuations whichcould stimulate the ship structure to vibrate.

FIG. 2 shows one option for the implementation of the first filters. Theregulator 10 contains, on the input side, a proportional regulator 33,which is connected on the input side to the addition point 9 and isconnected on the output side to an input of an integral regulator 34.The output of the integral regulator 34 is connected to an input of anaddition point 35, whose other input is connected to the output of theproportional regulator 33. The output of the addition point 35 forms theoutput of the regulator, to which the connecting line 11 is connected. Afeedback resistance 36 leads from the line 11 to the input of theregulator 33, feeding the output signal back in antiphase to the input.

A regulator designed in such a way has, when seen overall, alow-pass/amplification response, which is able at least to reduce theripple caused by the torque fluctuations from the ship's propeller 4.

The feedback resistance 36 varies the overall gain. In the event of anyerror between the rotation speed actual value n and a rotation speednominal value n*, the modified rotation speed nominal value n* isvirtually reduced by a value n_(R)=R×I*, when the actuating device 6produces a finite current nominal value I*, in order to produce anopposing torque.

In consequence, the actuating device 6 tries to regulate itself only tothe correspondingly reduced rotation speed nominal value n*−n_(R), thusproviding the propeller motor 3 with the opportunity, by reducing n fromn* into n*−n_(R), to release flywheel energy from the propulsion run,comprising the propeller motor 3, the ship's propeller 4 and thepropeller shaft 17. In the process, the closed-loop control device 2compares the falling motor rotation speed n virtually with a fallingrotation speed nominal value n*−n_(R)and in consequence scarcely needsto carry out any opposing control action. In consequence, the propellermotor 3 does not produce any additional torque, or produces only a smallamount of additional torque, so that no increased torque is introducedinto the ship's hull at the major anchoring point.

As soon as the propeller blades have assumed a different position, theload on the propeller shaft 17 falls, and the rotation speed n risesonce again, without increasing the motor torque. Since the rotationspeed actual value n is now greater than the virtual rotation speednominal value n*−n_(R), the amplitude of the regulator output signalfalls, and the system reverts to the initial operating point. Since therotation speed during a cycle such as this can flex only downward, themean value of the rotation speed n falls somewhat in comparison to theactual constant rotation speed nominal value n*, which is evident as apermanent control error of approximately 0.2 to 3%. In order tocounteract this effect, a compensation circuit may be inserted in thereference variable channel, that is to say between the control lever 1and the addition point 9, shifting the rotation speed nominal value n*virtually upward by a corresponding amount. In this case, particularlyin the case of ship propellers, it is possible to make use of the factthat the load torque of the propeller 4 rises approximately with thesquare of its rotation speed n so that, in consequence, the fed backsignal, which is fed back via the resistance and is approximatelyproportional to the drive torque of the propeller motor 3 in the steadystate, is also approximately identical to the rotation speed nominalvalue n*, as a square-law function of the rotation speed mean value n˜.The compensator accordingly has to have a branch which rises with thesquare of the rotation speed nominal value n*.

The line 13 may contain a function transmitter 37 in a correspondingway, which produces the compensation described above and supplies it asa signal N_(L)* to an addition point 38 in the line 7. In consequence,the rotation speed nominal value n* is raised by a value n_(L)* f(n).Thus, in the steady state, n_(L)*=−n_(R) and this has the desired effectthat the sum of the signal 8 and the signal 35 is equal to the signal 6at the addition point 9.

In the embodiment shown in FIG. 2, the fluctuations in the regulatoroutput signal, which are proportional to the torque, are fed back with aphase shift of approximately 180° to the rotation speed regulator inputthus resulting firstly in negative feedback and hence stable feedback,and secondly in the torque which is required to regulate out theload-dependent fluctuations in the rotation speed, and the regulatoroutput signal which is approximately proportional to this, beingreduced. The primary consequence of this is that the fluctuations in thedrive torque can be considerably reduced, so that the torquefluctuations emitted via the motor anchoring to the ship's hull and thetorque fluctuations which are emitted via the ship's propeller to thewake field of the ship's propeller can be reduced to non-criticalvalues.

One side effect in this case is that the rotation speed of the propellernow no longer remains exactly constant, but is subject to certainfluctuations, as caused by the alternating load. However, this is ofvery minor importance for the propulsion that is produced by thepropeller while, on the other hand, it is in this case possibleadvantageously to use the moment of inertia of the rotor of the electricmotor, of the propeller and the shaft to damp these fluctuations. Sincethe rotating bearings for the shaft have virtually no friction, theship's hull is not stimulated by these rotation speed fluctuations.

From the hydromechanical point of view, this effect has the majoradvantage that the rotation speed of the propeller now no longer remainsexactly constant but is subject to certain fluctuations which are causedby the alternating loads on the propeller. In consequence, this reducesthe fluctuation width resulting from the hydromechanical coupling of thewake field to the angle of advance. This reduction in the fluctuationwidth of the angle of advance results from the fact that the fluctuationin the load on that propeller blade which is located in theinhomogeneous wake field of the skeg or propeller-shaft stay that islocated on the ship's hull leads to a change in the rotation speed byvirtue of the above effect of an embodiment of the invention.

On the basis of its direction and magnitude, the change counteracts thecause. This leads to a change in the rotation speed and thus to dampingof the fluctuation width of the angle of advance of that propeller bladewhich is most at risk of cavitation. The reaction from this propellerblade on the other blades of the propeller resulting from the describedeffect is of minor importance, since their operating points remainconsiderably closer to the rated operating point of the propeller thanthe operating point of that propeller blade which is located in theinhomogeneous part of the wake field of the skeg or propeller-shaft staythat is provided on the ship's hull.

It is within the scope of the embodiments of the invention for the fedback output signal from the rotation speed regulator to be multiplied bya factor. This feedback should not, of course, be chosen to be toostrong since, otherwise, the approximately constant mean value of thedrive torque, which is likewise fed back, would result in an excessivereduction in the rotation speed nominal value occurring, so that therotation speed regulator would itself no longer be able (assuming thatthis rotation speed regulator has a PI characteristic) to accelerate thepropulsion shaft to the selected rotation speed nominal value. Since, onthe other hand, a predetermined voltage range is available both for theregulator input signal and for its output signal, for example from −10 Vto +10 V, with each of these limits corresponding to the maximumrotation speed for forward propulsion and propulsion astern, and to themaximum motor torque, multiplicative matching of these two signal levelsis essential for setting the optimum feedback level.

The multiplication factor may be between 0.01% and 5%, preferablybetween 0.1% and 3.0%, and especially between 0.15% and 2%. This isnegative feedback that is naturally at a very low level since—as alreadymentioned above—the majority of the power which is required by thechanging load can actually be provided by the moment of inertia of therotor of the electric motor, of the propeller and of the propulsionshaft and can in each case be fed back once again to it.

Since embodiments of the invention can result in a certain amount offreedom for rotation speed fluctuations, the propulsion run mayadvantageously be used as an energy store which, in a similar way to theenergy storage capacitor in an electrical power supply, leads tosmoothing of the power consumption from the electrical power supplynetwork for the propulsion system. A small amount of negative feedbackthus leads to the significant result that the torque applied by thepropulsion motor is largely smoothed without this causing anysignificant, permanent control error from the preselected nominal value.

With regard to the amount of negative feedback, a setting has beenproven in which the steady-state control error is between approximately0.2% and 2% at the rated load. In this case, despite the negativefeedback of the regulator output signal, the closed-loop control qualityis not adversely affected, in particular the dynamic response to changesin the rotation speed nominal value.

One compensation method which is preferred by an embodiment of theinvention uses the estimated, mean load on the propulsion as an outputvariable, and attempts to determine the steady-state control error to beexpected by mechanical recording of the path parameters from this, andto compensate for this control error by appropriate, reciprocaladjustment of the rotation speed nominal value.

In many cases, in particular also in the case of propeller propulsionsystems for ships, the characteristics of the controlled system are atleast approximately known. In particular, the steady-state, mean loadtorque based on a characteristic is obtained from the steady-staterotation speed actual value. By way of example, in the case of propellerpropulsion systems, the drive torque rises approximately with the squareof the rotation speed actual value. If the rotation speed actual valueis thus intended to correspond to a specific rotation speed nominalvalue it is possible to use this characteristic to determine,approximately, that torque which is approximately proportional to theregulator output signal in the steady state. Thus, the mean value of thefed back signal, and hence the residual control error, can also bedetermined. This is superimposed on the nominal value, preferablyadditively, thus resulting in the ideal rotation speed nominal value asthe rotation speed actual value itself when control errors that havebeen calculated in advance occur.

Owing to the reduction in the oscillation amplitude, there is no needfor expensive reinforcement of the ship's hull in the region of criticalpoints calculated using the finite element method. This results in aconsiderable reduction in the computation complexity and design effort,as well as in considerable material savings and in the assembly timebeing shortened.

The filters for suppression of the oscillations in the ship's hullresulting from the inhomogeneities during revolution of the ship'spropeller 4 may also be suppressed via a classic low-pass filter. Thecut-off frequency of the low-pass filter is in this case expedientlyreadjusted as a function of the rotation speed of the propeller shaft17. The aim of this is to additionally suppress low-frequency componentsat low propeller rotation speeds without adversely affecting theclosed-loop control system dynamic response, in consequence, at highrotation speeds. The rotation speed of the ship's propeller 4 stillpasses through a range of more than two powers of ten. In somecircumstances, a fixed cut-off frequency is not sufficient. A low-passfilter such as this can be produced by a digital solution, with thefiltering being carried out by a convolution function with a suitablecut-off frequency.

Instead of carrying out the filtering process in the frequency domain,the ripple can also be suppressed by carrying out the filtering processin the amplitude domain. FIG. 3 shows, schematically, the signal whichis produced at the output of the PI regulator 10 without any filtering.As shown, this is composed of a steady-state component and thesuperimposed ripple, which has already been mentioned a number of times.

The filtering is carried out by using a microprocessor and the programcontained in it to determine a lower limit 39, which is below thetroughs of the oscillation amplitude of the ripple. An upper limit 40 isdefined, matching this lower limit 39, with a certain safety margin fromthe peaks of the ripple. As long as the incoming signal is between thesetwo limits 39 and 40, a previously defined mean value, for example themean value between the limits 39 and 40, is passed to the control input12. Appropriate readjustment is carried out only when one of the limits39, 40 is infringed as a result of a greater error occurring due tomovement of the control lever 1.

Such amplitude filtering can be carried out particularly easily using amicroprocessor. However, it is also possible to use a nonlinearamplification characteristic for this purpose, such as that provided bya diode for example. An amplitude filter such as this is expedientlyaccommodated between the addition node 9 and the input of theproportional regulator 33.

The nonlinear transmission relationships result in the ripple in theregion of the zero being suppressed, while large signals are passedthrough.

FIG. 4 shows a highly schematic block diagram of a ship propulsionsystem according to the invention, in which second filter means 41 areimplemented, which are used to match the possible dynamic response fromthe actuating device and propeller motor to the possible and permissiblepropulsion dynamic response of the ship's propeller 4. Cavitationphenomena on the ship's propeller during acceleration processes are thussuppressed.

Where functional groups that have already been explained above occur inthis block diagram, these will not be described once again, and thereference symbols from the previous figures are used for thesefunctional groups. The first filter and the compensation circuit havebeen omitted from FIG. 4, for reasons of simplicity.

The second filter 41 for the ship propulsion system as shown in FIG. 4includes a ramp-up transmitter 42. The ramp-up transmitter 42 is locatedin the connecting line 7 which connects the control lever 1 to thenominal value input 8 of the addition node 9. The second filters 41 arethus located in a reference variable channel.

Another component of the second filter 41 is a characteristictransmitter 43, which is connected to a control input 44 of the ramp-uptransmitter 42 via a line 45. On the input side, the characteristictransmitter 43 is connected to the output of a circuit assembly 46, towhose input side the rotation speed signal is supplied from theconnecting line 13. The circuit assembly 46 is used to produce themagnitude of the rotation speed signal. The purpose of the second filter41 is to limit the rate of change of the nominal value signal, as itarrives from the control lever 1, to values which ensure that the ship'spropeller does not produce foam and has no tendency to cavitate.Irrespective of how quickly the control lever 1 is moved in the sense ofacceleration, the nominal value at the appropriate input of the additionelement 9 moves only at a lower rate.

Filters such as these can preferably be produced on a microprocessorbasis. In order to achieve the desired limiting, the signal coming fromthe control lever 1 may, for example, be differentiated, limited inaccordance with the characteristic transmitter 43 and then integratedonce again, in order to obtain the basic signal, but whose rate of risehas now been changed.

For this reason, the characteristic transmitter 43 receives a signalwhich is dependent on the rotation speed, because the limiting of therate of change is thus dependent on the ramp-up time for the rotationspeed of the ship's propeller 4. The magnitude of the actual rotationspeed of the propeller shaft 17 is used as a reference variable for theadaptive characteristic transmitter 43, and is hence indirectly used asa reference variable for the rate of rise of the nominal value signalwhich is passed on to the closed-loop control device 2.

FIG. 5 shows the profile of the characteristic for the second filter 41.It can be seen from this that the characteristic is continuous, that isto say it has no discontinuities, and is approximated by a string ofpolygons. The characteristic 47 for normal operation is composed ofthree sections 48, 49 and 50, which are plotted against the actualrotation speed of the ship's propeller 4.

In the illustrated exemplary embodiment, the lower actual rotation speedrange 48 extends from 0 to 46 rpm (up to approximately ⅓ of the ratedrotation speed), the central actual rotation speed range 49 extends from46 to 70 rpm (up to approximately half the rated rotation speed), andthe upper actual rotation speed range 47 extends from 70 to 150 rpm (upto the maximum rotation speed).

As can be seen from FIG. 5, a constant, short ramp-up time in the orderof seconds per rpm is predetermined in the characteristic transmitter 43for the adaptive ramp-up transmitter 42 for the low actual rotationspeed range 48 of the electric propeller motor 3, which may correspond,by way of example, to the range between 0 and ⅓ of the rated rotationspeed. The electric propeller motor 3 and hence the ship's propeller 4can operate with a high dynamic response in this maneuver range.

For the central actual rotation speed range 49, in FIG. 5, of theelectric propeller motor 3, which is located approximately between 113and half of the rated rotation speed of the electric propeller motor 3,the ramp-up time rises with a comparatively shallow gradient. Betweenthe two limits of this central actual rotation speed range 49, thecharacteristic transmitter 43 of the adaptive ramp-up transmitter 42changes into the propulsion mode, which corresponds to the higher actualrotation speed range 47 of the electric propeller motor 3. There, theramp-up time rises with increasing actual rotation speed of the electricpropeller motor 3 at a steeper gradient than in the central actualrotation speed range 49. Here, the characteristic transmitter 43 for thesecond filter 41 is given an even longer ramp-up time. The ramp-up timewhich is dependent on the rotation speed, allows the electric propellermotor 3 to be accelerated uniformly, without any current limit. Thisresults in continuous ship acceleration, as is shown in FIG. 6. Thisacceleration curve has no discontinuities.

For deceleration processes, it is advantageous to be able to preset aconstant ramp-down time in the second filter 41 and this may be, forexample, 0.2 s per rpm.

The configuration of the characteristic 47 allows the acceleration ofthe electric propeller motor 3, and hence that of the ship's propeller 4as well, to be varied freely. From the hydrodynamic point of view, thisresults in the major advantage that the operating point of the ship'spropeller 4 can be influenced in an advantageous manner by optimummatching of the acceleration in the higher rotation speed range, orpropulsion mode, 47. Thus, even during acceleration, the operating pointof the ship's propeller 4 can be kept away from areas of undesirable, oreven damaging, cavitation. This is a major financial advantage, sincecavitation on a ship's propeller 4 leads to considerable noise, whichconsiderably reduces the useful value in particular of passenger ships,research ships and naval ships.

Different characteristics for the ramp-up time may be stored in thecharacteristic transmitter 43 for the second filter 41. For example,FIG. 5 shows a characteristic 51 for an emergency maneuver in the regionthat is partially in the form of a dashed line, and which differs fromthe characteristic 47 for normal operation. Rapid acceleration can beallowed by selecting the characteristic 51 for emergency maneuvers, forexample by operating a button on the characteristic transmitter 43. Theramp-up time to the ship's maximum speed for a ship which is propelledby the propulsion device according to the invention can thus, by way ofexample, be reduced by half, with the characteristic 51 for emergencymaneuvering taking account exclusively of technically dependent limitvalues. In contrast, by way of example, the configuration of thecharacteristic 47 includes further aspects, with the configuration ofthis characteristic generally being chosen as a compromise betweenadequate ship maneuvering characteristics and operation of the entiremachine system in a conservative manner. Optimization is possible withrespect to various target functions such as minimum fuel consumption,minimum time passing, high ship maneuverability, etc. in alternativeprofile for the section 48 of the characteristic 47 in thecharacteristic transmitter 43 for the second filter 41 is a slightgradient which, however, is less than the gradient of the section 49.

It is also feasible for the characteristic in the characteristictransmitter 43 to be allowed to rise in accordance with the square lawas the rotation speed of the propeller motor 3 increases and, inaddition, to slightly emphasize a constant offset so that a shortramp-up time is actually set when the propeller motor 3 is rotating atlow rotation speeds. A further alternative is to omit the circuitassembly 46 for the second filter, and to extend the characteristictransmitter 43 by adding the negative rotation speed range of thepropeller motor.

If a ship is equipped with two propulsion devices according to anembodiment of the invention as described above, the load distributionbetween the two propeller shafts 17 of the electric propeller motors 3is controlled via the adaptive ramp-up transmitters 42. The propellershaft 17 with the lower load applied in this case has a somewhat loweractual rotation speed than the propeller shaft 17 to which the higherload is applied. In the higher actual rotation speed range 50, that isto say in the region of the propulsion mode of the electric propellermotor 3 or of the electric propeller motors 3, the adaptive ramp-uptransmitter 42 with the lower rotation speed actual value alwaysaccelerates faster than the adaptive ramp-up transmitter 42 with thehigher rotation speed actual value. While the ship is accelerating, thisbehavior results in uniform load distribution between the two propellershafts 17, virtually automatically. This results in better directionalstability during acceleration.

The response of the second filter 41 of the propulsion device accordingto an embodiment of the invention indicates that it is possible to add adefinable acceleration torque to a steady-state load torque. Thisdefinable acceleration torque remains in the propulsion mode range, thatis to say it remains to a certain extent constant in the region of thehigher actual rotation speed range 47 of the electric propeller motor 3,and thus remains free of values which are unnecessarily high at times.By interaction with the first filter already described, and with thesecond filter 41 being readjusted, this has prevented, inter alia, thetendency of the ship's propeller 1 to cavitate or to produce foam.

Suitable circuits for readjustment of the ramp-up transmitter 42contained in the second filter 41, by the rotation speed regulator, areknown from the prior art. These are not illustrated in the figures, forreasons of simplicity.

FIG. 7 shows a highly schematic block diagram of a ship propulsionsystem according to the invention, which has third filters 55 which areused to match the possible dynamic response from the actuating deviceand propeller motor to the possible and permissible dynamic response ofthe generator system. In consequence, voltage and/or frequencyfluctuations in the on-board power supply network are suppressed duringacceleration and deceleration processes.

Where functional groups which have already been explained above occur inthis block diagram, these will not be described once again, and thereference symbols from the previous figures are used for thesefunctional groups. The first and second filters, and the compensationcircuit in FIG. 7, have been omitted for reasons of simplicity.

The on-board power supply network 5 is fed from a diesel generatorsystem 56 having four diesel generators 57 . . . 61. The generators arein this case normally three-phase synchronous generators.

The third filters 55 have a limiting circuit 62, which is locatedbetween the output of the regulator 10 and the control input 12 of theactuating device 6.

The purpose of the limiting circuit 62 is to allow the output signalfrom the regulator 10 to become larger or smaller depending on theamplitude, or to limit an excessively fast rate of rise. The limitingcircuit 62 has two control inputs 63 and 64, which are connected to anupper and a lower limit value stage 65 and 66. The upper and the lowerlimit stages define, via the control inputs 63 and 64, the rate at whichthe signal may vary in the upward or downward direction, respectively,and, furthermore, they have the characteristic of defining an amplitudewindow.

As long as the change in the amplitude of the output signal from theregulator 10 moves within this window, the rate of change is notinfluenced by the limiting circuit 62. The limiting circuit 62 starts toact only when the amplitude of the output signal from the regulator 10varies more sharply than is defined by the two limit value stages 65 and66.

The center and the size of the amplitude window, which is defined by thetwo limit value stages 65 and 66, are not rigid, for which reason thetwo limit value stages 65 and 66 have control inputs 67, 69. The controlinputs 67, 69 are connected to one output of a characteristictransmitter 72 which has two control inputs 73 and 74, via which theramp-up time and the ramp-down time are define. The input 74 isconnected via an appropriate line to the control input 12, and thusreceives information about the instantaneous value of the referencevariable, which is passed to the actuating device 6.

The input 73 is connected to one output of a further characteristictransmitter 75, into which, firstly, the magnitude of the rotation speedsignal as it arrives from the circuit assembly 45 and, on the otherhand, a control signal from a logic circuit 76, are fed. The logiccircuit 76 is connected via a control line 77 to switches 78, 79, 81 and82, via which the individual generators 57 . . . 61 are connected to theon-board power supply network 5. The characteristic transmitter 75defines the ramp up time and the ramp-down time for the ramp-uptransmitter 72.

The size of the amplitude window, which is likewise defined by the twolimit value stages 65 and 66, is not rigid, for which mason the twolimit value stages 65 and 66 have control inputs 98, 99. The controlinputs 98, 99 are connected to one output of a further characteristictransmitter 97, into which, on the one hand, the magnitude of therotation speed signal as it arrives from the switching assembly 45already described above, and on the other hand a control signal are fed,as made available by the logic circuit 76 which has already beendescribed above.

The limit value stage 65 is expediently an adder, and the limit valuestage 66 is a subtractor. The output from the ramp-up transmitter 72produces the steady state of the torque-forming control signal, as ispassed to the control input 12 of the actuating device 6. The output ofthe characteristic transmitter 97 produces the maximum sudden signalchange in the torque-forming control signal that is permissible withrespect to the steady state at the respective operating point, as ispassed to the control input 12 of the actuating device 6.

The third filters 55 thus define the maximum permissible rate of changeat which the nominal value signal for the actuating device 6 may vary,and hence by which the rotation speed of the propeller motor or motors 3may vary, to be precise as a function of the rotation speed of thepropeller motor 3, and of the number and load on the diesel generatorswhich are connected to the on-board power supply network. A time changeis carried out in conjunction with the limit value stages 65 and 66,that is to say the signal rate of change is influenced, but only whenthe signal change exceeds an amount which is defined in the limit valuestages. This window which is formed in this way is also dependent on thenumber of diesel generators 57 . . . 61 which are connected to theon-board power supply network 5, on the rotation speed of the propellermotor 3 and on the magnitude of the control signal for the actuatingdevice 6.

In this way, the rate of change of the power consumption by thepropeller motor or motors 3 is restricted to values which the dieseldrives for the diesel generators 57 . . . 61 and/or the field excitationof the synchronous generators can follow without this leading toexcessive voltage fluctuations and/or frequency fluctuations in theon-board power supply network 5.

In order that the ship can still be maneuvered well and in order that nocontrol oscillations whatsoever occur either, an amplitude region of thesignal which is located around the instantaneous value of the controlsignal of the input 12 is, however, uninfluenced by the limit to therate of rise or rate of fall. If this were not done, there would be arisk of the change in the instantaneous value (caused by the closed-loopcontrol of the drive) resulting from the rate of change limit, leadingto control oscillations, and hence to beating in the drive.

The third filters are thus used to preset a ramp-up time and a ramp-downtime for the reference variable, which is passed to the control input12. The maximum permissible time loading of the diesel engines, andremoval of load from the diesel engines, in the diesel generator systemare taken into account when selecting these times. In order to takeaccount of this, the ramp-up time and ramp-down time which are definedin the third filters 55 vary in proportion to the magnitude of therotation speed of the propeller motor 3. The times may possibly alsovary on the basis of the load at any given time on the diesel engines inthe generator system.

FIG. 8 shows a characteristic 83 which is provided by the characteristictransmitter 75 when only a single diesel generator is connected to theon-board power supply network 5.

As can be seen, a minimum ramp-up time and ramp-down time are defined(horizontal straight section) in a lower rotation speed range of theelectric propeller motor, which corresponds approximately to themaneuvering region, that is to say ending at approximately ⅓ of therated rotation speed. This ramp-up time and ramp-down time are governedby the maximum permissible rate of change in the wattless componentemitted by the synchronous generator in the diesel generator that isswitched on. As the rotation speed of the propeller motor 3 increases,the rate of change falls, that is to say the maximum permissible timewithin which the power consumption or emission of the diesel engines inthe generator system may vary, becomes longer, as can be seen from therising branch of curve 83 in FIG. 8.

When the on-board power supply network 5 is being fed from two dieselgenerators, a curve 84 is used. As can be seen in FIG. 8, this curve islocated below the curve 83, that is to say faster power changes arepossible both in the horizontal part of the curve and in the risingpart.

If even more generators are connected, the curves 85 and 86,respectively, apply respectively to three or four diesel generators 57 .. . 61 which are switched on at the same time.

It is, of course, generally not expedient to start the propulsion loadwith all the diesel generators 57 . . . 61 from the start. If the dieselgenerators 57 . . . 61 are connected successively, as a function of therotation speed of the propeller motor 3, that is to say as a function ofthe total power consumption of the ship propulsion system, this resultsin the permissible power rate of change having the profile shown in FIG.9.

The left-hand horizontal section, including the left-hand rising branchwith the reference symbol 87, corresponds to the corresponding part ofthe curve 84 with only two diesel generators. Beyond a certain rotationspeed, which corresponds to a corresponding power consumption, a thirddiesel generator is connected, so that the rate of change of the powerconsumption is defined by a curve 88, into which the curve 87 mergessuddenly. If the power consumption is even greater, the fourth dieselgenerator is finally also connected, so that the power may change inaccordance with a curve 89.

The maximum permissible rate of change of the reference variables, asappropriate at the input 12, has an approximately sawtooth profile and,by connection of diesel generators, is kept approximately at a value(even in the high power range) which corresponds to maneuvering withonly two active diesel generators.

In the quasi-steady state, the regulator 10 must be able to control thenominal value to be passed on to the actuating device 6, free of anylimits. Otherwise, as already mentioned above, severe beating wouldoccur in the electric propeller motor 3, which could become evident asmechanical oscillations in the ship. These can also promote or initiatecavitation on the ship's propeller 4. The limit to the rate of changetherefore does not operate within the abovementioned amplitude window.

If the amplitude change remains independent of the rate of change withinthis window, the third filters 55 have no effect. Since the regulator 10and hence also the actuating device 6 operate with their full dynamicresponse for this range, voltage fluctuations can occur in the on-boardpower supply network 5 since the excitation of the synchronousgenerators in the diesel generator system 56 cannot follow thissufficiently quickly. The actuating device 6 which, as alreadymentioned, operates as a frequency changer or converter, produces areactive current which leads to voltage fluctuations due to thereactance of the synchronous generators. For this reason, the size ofthe window is set such that the reactive current which results from thepower changes and flows into the on-board power supply network producesa voltage drop across the reactance of the generators that areconnected, with this voltage drop in all cases being within the maximumpermissible voltage tolerance of the on-board power supply network 5.Very rapid voltage fluctuations within the permissible voltage tolerancefor the on-board power supply network 5 are thus not critical to itsoperation.

The separation between the lower and upper edge of the window and theinstantaneous value of the nominal value of the control input 12 is afunction of the magnitude of the rotation speed of the propeller motor3, since the power factor on the on-board power supply network sidedepends on the drive level of the respective actuating device 6.Furthermore, the size of the window is proportional to the number ofsynchronous generators in the diesel generator system 56 which arefeeding the on-board power supply network 5. The reason for this is thehigher short-circuit rating in the on-board power supply network, whichin turn is a result of the smaller reactance of the parallel-connectedsynchronous generators.

FIG. 10 shows the variation range of the window for the nominal value atthe control input 12 for the situation where the current drawn by thepropeller motor 3 is not dependent on the rotation speed The smallestwindow, which is fixed between the two curve runs 91, applies to thesituation where only one diesel generator is connected to the on-boardpower supply network. A somewhat larger window, corresponding to twocurves 92, is obtained when there are two diesel generators, while thewindow widens, corresponding to the distance between the two curves 93for two diesel generators to become a window corresponding to two curves94 when there are a total of four diesel generators feeding the on-boardpower supply network 5. FIG. 11 shows, schematically, the width of thewindow when the propulsion power can be varied as a function of therotation speed of the propeller motor 3. The width of the window isrepresented by two dashed curves 95.

The curves start at a low rotation speed with two diesel generatorsconnected. A further diesel generator starts to operate at the firstdiscontinuity point coming from the left, while four diesel generatorsare operated to the right of the second discontinuity point.

Furthermore, it may be expedient for the ramp-up time and ramp-down ofthe nominal value at the control input 12 to be varied as a function ofthe operating state of the diesel generator system which is feedingelectrical power to the on-board power supply network, in which casedifferent diesel generators of the diesel generator system may be usedin different operating states.

The specific arrangement of the third filter 55 at the output of theregulator 10 also suppresses excessively rapid control processes whichare not caused by the movement of the control lever 1 but by loadchanges on the ship's propeller 4. Load changes occur when rudder isapplied or the rudder is moved back to the null position. The loadchanges result in rotation speed changes which must be regulated out andlead to a different power consumption. The regulator 10 is intrinsicallyvery fast, and could possibly overcontrol the on-board power supplynetwork, if it were not limited by the third filter 55.

It is self-evident that the three described filters may be used in anydesired combination with one another.

The filters and the closed and open control loops have been describedabove in the form of classic electrical outline circuit diagrams, inorder to make it easier to understand them. However, it is self-evidentthat, when implemented in practice, the filters and the closed and opencontrol loops are generally in the form of programs or program sections.The nature of the description is not intended to imply any restrictionto the specific type of practical implementation since it is clear tothose skilled in the art how filters and regulators can be configured indigital form, as programs. Above all, the digital implementation hasadvantages for closed-loop control systems with long time constants orvariable time constants.

A ship propulsion system includes an electrical on-board power supplynetwork and an electrical propulsion system which is fed from it has asubordinate closed-loop control system for the propeller motor. Therotation speed of the propeller motor is governed by a higher-levelregulator, whose reference variable comes from the control lever. Filtermeans are included, in order to suppress adverse effects on theoperation of the ship resulting from the propulsion system having anexcessively high dynamic response.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A ship propulsion system for a ship including anelectrical on-board power supply network, comprising: a control leverarrangement, including a control lever, adapted to emit a control leversignal corresponding to the position of the control lever, a source forproduction of electrical power, an electrical actuating device,including a power input, a power output and a control input, wherein thepower input is connected to the source; an electric propeller motor,adapted to drive a ship's propeller and connected to the power output ofthe actuating device; a rotation speed sensor, adapted to emit arotation speed signal corresponding to the rotation speed of the ship'spropeller; a regulator device, including a regulator output, a nominalvalue input and an actual value input, wherein the control lever signalis fed into the nominal value input and the rotation speed signal is fedinto the actual value input, and wherein the regulator output isconnected to the control input of the actuating device; and filter meansfor suppressing rates of change of instantaneous values of theelectrical power, emitted by the actuating device to the propellermotor, which cause adverse effects on the ship operation.
 2. The shippropulsion system as claimed in claim 1, wherein the instantaneous valueincludes at least one of the value of a DC voltage and the root meansquare value of an AC voltage.
 3. The ship propulsion system as claimedin claim 1, wherein the instantaneous value is the frequency of an ACvoltage.
 4. The ship propulsion system as claimed in claim 1, whereinthe adverse effects include oscillations in the ship's hull, caused bytorque fluctuations from the propeller motor.
 5. The ship propulsionsystem as claimed in claim 1, wherein the adverse effects include atleast one of voltage spikes and frequency fluctuations in the on-boardpower supply network, caused by excessively fast movement of the controllever in the sense of reducing the rotation speed of the propellermotor.
 6. The ship propulsion system as claimed in claim 1, wherein theadverse effects include at least one of voltage spikes, voltage dips andfrequency fluctuations in the on-board power supply network, caused byload changes on the propeller caused by at least one of ruddermovements, changes to the propeller pitch and, in the case of ships withother propulsion runs, changes to the rotation speed of anotherpropulsion run.
 7. The ship propulsion system as claimed in claim 1,wherein the adverse effects are formed by dynamic changes to the ship'spropeller as a function of the speed of motion.
 8. The ship propulsionsystem as claimed in claim 1, wherein the filter means include firstfilter means for suppressing amplitude fluctuations in the signal at thecontrol input, when at least one of the frequency of the amplitudefluctuations is above a predetermined limit, and the amplitude of theamplitude fluctuations is below a predetermined limit.
 9. The shippropulsion system as claimed in claim 8, wherein the first filter meansinclude amplitude filters.
 10. The ship propulsion system as claimed inclaim 8, wherein the first filter means include frequency filters. 11.The ship propulsion system as claimed in claim 8, wherein the firstfilter means are located upstream of the actual value input, such thatthe actual value signal is supplied via the first filter means.
 12. Theship propulsion system as claimed in claim 8, wherein the first filtermeans are arranged between the regulator output and the control input.13. The ship propulsion system as claimed in claim 8, wherein the firstfilter means are integrated in the regulator device.
 14. The shippropulsion system as claimed in claim 8, wherein the first filter meansare designed to be adaptive, such that the respective filtercharacteristic value is dependent on the rotation speed of the ship'spropeller.
 15. The ship propulsion system as claimed in claim 8, whereinthe first filter means include a filter means control input into whichthe rotation speed signal is fed.
 16. The ship propulsion system asclaimed in claim 1, wherein the regulator device includes a PIcharacteristic.
 17. The ship propulsion system as claimed in claim 1,wherein at least one of the regulator device and the first filter meansis designed to operate in at least one of digital form, analog form andmixed analog/digital form.
 18. The ship propulsion system as claimed inclaim 1, wherein at least one of the regulator device and the filtermeans is in the form of a program in at least one of a microprocessorand a microcontroller.
 19. The ship propulsion system as claimed inclaim 1, wherein the regulator device includes, in series, aproportional regulator, an integral regulator and an addition element,with one input of the proportional regulator forming an input into whichthe closed-loop control difference is fed, one output of theproportional regulator being connected to one input of an integralregulator, and the output of the proportional regulator and the outputof the integral regulator being connected to inputs of the additionelement, whose output forms the regulator output and is fed back to theinput of the proportional regulator.
 20. The ship propulsion system asclaimed in claim 19, wherein the feedback is set such that it results ina steady-state closed-loop control error of approximately 0.2% to 2%.21. The ship propulsion system as claimed in claim 20, wherein thesteady-state closed-loop control error is compensated for by a correctednominal value n*.
 22. The ship propulsion system as claimed in claim 21,wherein a nominal value compensation n_(L)* is carried out as a functionof an estimated load.
 23. The ship propulsion system as claimed in claim22, wherein the estimated load is determined on the basis of acharacteristic from an uncompensated rotation speed nominal value. 24.The ship propulsion system as claimed in claim 1, wherein the actuatingdevice is in the form of a regulator, whose nominal value input formsthe control input for the actuating device.
 25. The ship propulsionsystem as claimed in claim 1, wherein the actuating device emits at itspower output, a DC voltage whose value is dependent on the position ofthe control lever.
 26. The ship propulsion system as claimed in claim 1,wherein the actuating device emits at its power output an AC voltage,whose frequency is dependent on the position of the control lever. 27.The ship propulsion system as claimed in claim 1, wherein the actuatingdevice is designed such that the current which the actuating deviceemits to the propeller motor is adjusted via the signal at the controlinput.
 28. The ship propulsion system as claimed in claim 1, wherein thefilter means includes second filter means including a controlled ramp-uptransmitter, which defines a ramp-up time within which the rotationspeed of the propeller motor follows the position of the control leverin the sense of acceleration as a function of a characteristic.
 29. Theship propulsion system as claimed in claim 28, wherein thecharacteristic is continuous in the sense that the characteristic has nodiscontinuities.
 30. The ship propulsion system as claimed in claim 28,wherein the second filter means are located between the control leverand the nominal value input of the closed-loop control device.
 31. Theship propulsion system as claimed in claim 28, wherein the second filtermeans includes a control input into which the rotation speed signal isfed.
 32. The ship propulsion system as claimed in claim 28, wherein theramp-up time is at least one of constant and short, and slightly risingand short, in the rotation speed range between 0 and approximately ⅓ ofthe rated rotation speed.
 33. The ship propulsion system as claimed inclaim 28, wherein the ramp-up time rises more sharply with the rotationspeed of the propeller motor for a rotation speed range of the propellermotor above ¼ of the rated rotation speed.
 34. The ship propulsionsystem as claimed in claim 33, wherein the ramp-up time rises even moresharply with the rotation speed of the propeller motor than for therotation speed range which is below half the rated rotation speed thanfor an upper rotation speed range of the propeller motor which is abovehalf the rated rotation speed.
 35. The ship propulsion system as claimedin claim 28, wherein the second filter means is designed to operate inat least one of digital form, in analog form, and in mixeddigital/analog form.
 36. The ship propulsion system as claimed in claim28, wherein a ramp-down time, which is predetermined in the secondfilter means, is at most equal to the ramp-up time, which is dependenton the rotation speed, in the rotation speed ranges of the propellermotor up to ¼.
 37. The ship propulsion system as claimed in claim 28,wherein a ramp-down time, which is predetermined in the second filtermeans, is at most constant as the rotation speed of the propeller motordecreases.
 38. The ship propulsion system as claimed in claim 28,wherein a ramp-down time, which is predetermined in the second filtermeans, is continuous, in the sense that it has no discontinuities. 39.The ship propulsion system as claimed in claim 28, wherein a ramp-downtime, which is predetermined in the second filter means, isapproximately 0.2 s per rpm.
 40. The ship propulsion system as claimedin claim 1, wherein the filter means includes third filter means whichlimit the rate of change of the power consumption by the propellermotor.
 41. The ship propulsion system as claimed in claim 40, whereinthe third filter means are set up to limit the rate of change of theoutput variable from the closed-loop control device for the electricalactuating device, taking into account limit values which are dependenton the source which feeds electrical power to the on-board power supplynetwork.
 42. The ship propulsion system as claimed in claim 40, whereinthe third filter means are designed such that they limit the rate ofchange of the output variable in one direction, which is referred to asat least one of a ramp-up time and ramp-up rate of change, to adifferent value than the rate of change of the output variable in theother direction, which is referred to as at least one of a ramp-downtime and ramp-down rate of change.
 43. The ship propulsion system asclaimed in claim 42, wherein at least either the value for the ramp-uptime or the value for the ramp-down time, which is or are limited by thethird filter means, can be varied in the same sense as the change in themagnitude of the actual rotation speed of the electric propeller motor.44. The ship propulsion system as claimed in claim 41, wherein, in alower rotation speed range of the electric propeller motor or of theship's propeller, a ramp-up time and a ramp-down time, which arepredetermined by the third filter means, are matched to a maximumpermissible rate of change of a wattless component emitted by the sourcewhich feeds the on-board power supply network.
 45. The ship propulsionsystem as claimed in claim 41, wherein the source includes at least twogenerators, and wherein at least one of a ramp-up time and a ramp-downtime, predetermined by the third filter means, are variable in theopposite sense to a change in at least one of the number and physicalsize of the active generators.
 46. The ship propulsion system as claimedin claim 41, wherein at least one of a ramp-up time and a ramp-downtime, predetermined by the third filter means, is variable as a functionof the operating state of the source.
 47. The ship propulsion system asclaimed in claim 41, wherein the third filter means are designed suchthat a window is provided, within which the limiting of at least one ofa ramp-up time and of a ramp-down time does not operate.
 48. The shippropulsion system as claimed in claim 47, wherein the position of thewindow is essentially synunetrical with respect to the output variable,at least in one range of the output variable from the closed-loopcontrol device, such that limiting occurs at approximately the same rateof change in both directions.
 49. The ship propulsion system as claimedin claim 47, wherein, in order to provide the window, the output signalfrom the closed-loop control device is fed back into a control input ofthe third filter means.
 50. The ship propulsion system as claimed inclaim 47, wherein the size of the window can be adjusted such that areactive current in the on-board power supply network, which resultsfrom the rate of change of the power consumption of the propeller motor,produces a voltage drop which is within the maximum permissible voltagetolerance of the on-board power supply network across a reactance of thesource.
 51. The ship propulsion system as claimed in claim 47, whereinthe source includes at least two generators, and wherein the size of thewindow is larger than the number of active generators.
 52. The shippropulsion system as claimed in claim 41, wherein a ramp-up time and aramp-down time of the current nominal value are varied in the same senseas the change in the magnitude of the actual rotation speed of theelectric propeller motor.
 53. The ship propulsion system as claimed inclaim 41, wherein a ramp-up time and a ramp-down time of the currentnominal value are varied in inverse proportion to the number andphysical size of the generators which feed electrical power into theon-board power supply network.
 54. The ship propulsion system as claimedin claim 41, wherein the third filter means are designed such that theyoperate on a microprocessor basis, in at least one of analog form and inmixed digital/analog form.
 55. The ship propulsion system as claimed inclaim 22, wherein the estimated load is determined on the basis of acharacteristic from the rotation speed actual value.
 56. The shippropulsion system as claimed in claim 1, wherein the filter meansincludes second filter means including a controlled ramp-up transmitter,which defines a ramp-up time within which the rotation speed of thepropeller motor follows the position of the control lever in the senseof acceleration as a function of the rotation speed of the propellermotor.
 57. The ship propulsion system as claimed in claim 28, wherein aramp-up time rises more sharply with the rotation speed of the propellermotor for a rotation speed range of the propeller motor above ⅓ of therated rotation speed.
 58. The ship propulsion system as claimed in claim28, wherein a ramp-down time, which is predetermined in the secondfilter means, is at most equal to a ramp-up time, which is dependent onthe rotation speed, in the rotation speed ranges of the propeller motorup to ⅓, of the rated rotation speed.
 59. The ship propulsion system asclaimed in claim 28, wherein a ramp-down time, which is predetermined inthe second filter means, is considerably shorter than a ramp-up time,which is dependent on the rotation speed, in the subsequent rotationspeed range of the propeller motor.
 60. The ship propulsion system asclaimed in claim 42, wherein at least either the value for the ramp-uptime or the value for the ramp-down time, which is or are limited by thethird filter means, can be varied in proportion to the magnitude of theactual rotation speed of the electric propeller motor.
 61. The shippropulsion system as claimed in claim 41, wherein the source includes atleast two generators, and wherein at least one of a ramp-up time and aramp-down time, predetermined by the third filter means, are variable ininverse proportion to at least one of the number and physical size ofthe active generators.
 62. The ship propulsion system as claimed inclaim 47, wherein the size of the window can be adjusted such that areactive current in the on-board power supply network, which resultsfrom the rate of change of the power consumption of the propeller motor,produces a voltage drop which is within the maximum permissible voltagetolerance of the on-board power supply network across a reactance of asynchronous generator.
 63. The ship propulsion system as claimed inclaim 41, wherein a ramp-up time and a ramp-down time of the currentnominal value are varied in proportion to the magnitude of the actualrotation speed of the electric propeller motor.